After twenty-five years I think it is safe for me to confess that I wrote both Search for the Sage and its sequel Tunnel at World's End when I was supposed to be working for the Exchequer and Audit Department (now the National Audit Office) in Chesser House, Edinburgh.
Search for the Sage was written just before my children were born, and the children in it are called Stephen, Pamela and Mary. If you can't work out where these names come from, you haven't been paying attention! My wife's nieces and nephews were enthusiastic first readers of Search for the Sage, and that is why the book is dedicated to "Toby, Lucy and Jenny, who went there first".
I added a fourth character in Tunnel at World's End, and called him Toby after the oldest nephew. By then my own children had put in an appearance, and that is why Tunnel at World's End is dedicated to "Philip, Michael and Sarah, who went there second."